This invention relates in general to vehicle safety devices and in particular to a new and useful device for retightening a safety belt which is held on a takeup roller.
Seat belt retighteners serve to eliminate the slack in a belt in a collision by pulling back the belt so that the free prolapse path of the seat belt until the belt becomes effective is as short as possible. Retighteners, which consist of a cylinder and a piston admitted with propellant gases are also called linear tighteners. A linear tightener can be seen, e.g. in German OS No. 24 11 702. Compared to rotary tighteners with rotary driving motors working on the rotary piston the linear tighteners have principally a simpler construction.
A winding attachment with a retightener must meet particularly three requirements. First, the retightener must be able to eliminate sufficiently large slack in the belt (e.g. 20 cm), it should be able to be accommodated in the small available space in motor vehicles, and third, it should be able to be arranged subsequently in existing standard automatic takeup rollers without, or at any rate with only minor changes.
A winding attachment using a movable piston moved by a pyrotechnic propellant gas has already been suggested. The cylinder for the piston is arranged above the automatic takeup roller and extends substantially vertically upward. The upper end of the cylinder is tapered to prevent the piston from issuing from the cylinder in case of an accident. The length of the cylinder corresponds for constructional reasons to a greater length than the slack to be eliminated and is, e.g. about 30 cm. Such a long cylinder is very difficult to accommodate in the B-column of today's automobiles. In order to make the cylinder even longer, the pyrotechnic composition is arranged in a separate housing which is axis parallel to the automatic takeup roller. Due to the arrangement of the propellant charge in a separate housing, the manufacturing costs of the known linear tightener are increased. In addition, the long cylinder tube prevents a compact construction.